High efficiency ceiling fan

ABSTRACT

Ceiling fan energy consumption efficiency is enhanced with fan blades that have an angle attack that decreases from root end to tip end at higher rates of decrease nearer their tip ends than at their root ends.

REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No.10/194,699 filedJul. 11, 2002.

TECHNICAL FIELD

This invention relates generally to ceiling fans, and specifically toelectrically powered ceiling fans and their efficiencies.

BACKGROUND OF THE INVENTION

Ceiling fans powered by electric motors have been used for years incirculating air. They typically have a motor within a housing mounted toa downrod that rotates a set of fan blades about the axis of thedownrod. Their blades have traditionally been flat and oriented at anincline or pitch to present an angle of attack to the air mass in whichthey rotate. This causes air to be driven downwardly.

When a fan blade that extends generally radially from its axis ofrotation is rotated, its tip end travels in a far longer path of travelthan does its root end for any given time. Thus its tip end travels muchfaster than its root end. To balance the load of wind resistance alongthe blades, and the air flow generated by their movement, fan bladeshave been designed with an angle of attack that diminishes towards thetip. This design feature is also conventional in the design of otherrotating blades such as marine propellers and aircraft propellers.

In 1997 a study was conducted at the Florida Solar Energy Center on theefficiencies of several commercially available ceiling fans. Thistesting was reported in U.S. Pat. No. 6,039,541. It was found by thepatentees that energy efficiency, i.e. air flow (CFM) per powerconsumption (watts), was increased with a fan blade design that had atwist in degrees at its root end that tapered uniformly down to asmaller twist or angle of attack at its tip end. For example, thisapplied to a 20-inch long blade (with tapered chord) that had a 26.7°twist at its root and a 6.9° twist at its tip.

Another long persistent problem associated with ceiling fans has beenthat of air flow distribution. Most ceiling fans have had their bladesrotate in a horizontal plane, even though oriented at an angle ofattack. This has served to force air downwardly which doesadvantageously provide for air flow in the space beneath the fan.However air flow in the surrounding space has been poor since it doesnot flow directly from the fan. Where the fan blades have been on adihedral this problem has been reduced. However this has only beenaccomplished at the expense of a substantial diminution of air flowdirectly beneath the fan.

SUMMARY OF THE INVENTION

It has now been found that a decrease in angle of attack or twist thatis of a uniform rate is not the most efficient for ceiling fans. The tipof a 2-foot blade or propeller travels the circumferences of a circle or2π(2) in one revolution. Thus its midpoint one foot out travels 2π(1) orhalf that distance in one revolution. This linear relation is valid foran aircraft propeller as its orbital path of travel is generally in aplane perpendicular to its flight path. A ceiling fan however rotates inan orbital path that is parallel to and located below an air flowrestriction, namely the ceiling itself. Thus its blades do not uniformlyattack an air mass as does an aircraft. This is because “replacement”air is more readily available at the tips of ceiling fan blades thaninboard of their tips. Air adjacent their axis of rotation must travelfrom ambience through the restricted space between the planes of theceiling and fan blades in reaching their root ends.

With this understanding in mind, ceiling fan efficiency has now beenfound to be enhanced by forming their blades with an angle of attackthat increases non-uniformly from their root ends to their tip ends.More specifically, it has been found that the rate of change in angle ofattack or pitch should be greater nearer the blade tip than nearer itsroot. This apparently serves to force replacement air inwardly over thefan blades beneath the ceiling restriction so that more air is morereadily available nearer the root ends of the blades. But whether or notthis theory is correct the result in improved efficiency has beenproven. By having the change in angle of attack at a greater rate attheir tip than at their roots, fan efficiency has been found to besubstantially enhanced.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side view of a ceiling fan that embodies the invention inits preferred form.

FIG. 2 is a diagrammatical view of a fan blade of FIG. 1 shownhypothetically in a planar form for illustrative purposes.

FIG. 3 is a diagrammatical view of the fan blade of FIG. 2 illustratingdegrees of blade twist at different locations along the blade.

FIG. 4 is a diagram of air flow test parameters.

FIG. 5 is a side view of one of the blades of the fan shown in FIG. 1.

FIG. 6 is a top view of one of the blades of the fan shown in FIG. 1.

FIG. 7 is an end-on view of one of the blades of the fan shown in FIG.1.

FIG. 8 is a perspective view of a ceiling fan that embodies theinvention in another preferred embodiment.

FIG. 9 is a diagrammatical view of a fan blade of FIG. 8 shownhypothetically in a planar form for illustrative purposes.

FIG. 10 is a series of diagrammatical view of the fan blade of FIG. 8illustrating degrees of blade twist at different locations along theblade.

DETAILED DESCRIPTION

The fan blade technology disclosed in U.S. Pat. No. 6,039,541 followedthe assumption that all air flow into the fan blades is from a directionthat is perpendicular to the plane of rotation for the blades. Inaddition, it assumed that the airflow is of a constant velocity from theroot end to the tip end of the blades as used in aircraft propellertheory. Using this assumption the blades were designed with a constanttwist rate from root end to tip end.

Twisting of the blade is done in an attempt to optimize the relativeangle of attack of the airflow direction relative to the blade surface.This is done to ensure that the blade is operating at its optimum angleof attack from root end to tip end. This angle changes to accommodatethe fact that the tip of the blade moves faster than the root end of theblade diameter. This increase in velocity changes the direction of therelative wind over the blade.

Again, this assumption has now been found to be invalid for ceilingfans. Ceiling, fans are air re-circulating devices that do not movethrough air as an aircraft propeller does. Air does not move in the samevector or even velocity over their blades from root end to tip end.

FIG. 1 illustrates a ceiling fan that is of conventional constructionwith the exception of the shape of its blades. The fan is seen to bemounted beneath a ceiling by a downrod that extends from the ceiling toa housing for an electric motor and switch box. Here the fan is alsoseen to have a light kit at its bottom. Power is provided to the motorthat drives the blades by electrical conductors that extend through thedownrod to a source of municipal power.

The fan blades are seen to be twisted rather than flat and to have agraduated dihedral. Air flow to and from the fan blades is shown by themultiple lines with arrowheads. From these it can be visuallyappreciated how the fan blades do not encounter an air mass as does anairplane propeller. Rather, the restricted space above the blades altersthe vectors of air flow into the fan contrary to that of an aircraft.

Each fan blade is tapered with regard to its width or chord as showndiagrammatically in FIG. 2. Each tapers from base or root end to tip endso as to be narrower at its tip. In addition, each preferably has adihedral as shown in FIG. 1 although that is not necessary to embody theadvantages of the invention. The dihedral is provided for a widerdistribution of divergence of air in the space beneath the fan.

With continued reference to FIGS. 2 and 3 it is seen that the blade isdemarked to have three sections although the blade is, of course, ofunitary construction. Here the 24-inch long blade has three sections ofequal lengths, i.e. 8 inches each. All sections are twisted as isevident in FIG. 1. However the rate of twist from root to tip isnonuniform. The twist or angle of attack deceases from root end down to10° at the tip end. This decrease, however, which is also apparent inFIG. 1, is at three different rates. In the first 8-inch sectionadjacent the root end the change in twist rate is 0.4° per inch. For themid section it is 0.7° per inch. For the third section adjacent the tipit is at a change rate of 1.0° per inch. Of course there is a smalltransition between each section of negligible significance. Thus in FIG.3 there is an 8° difference in angle of attack from one end of theoutboard section to its other (1° per inch×8 inches). For the midsection there is about 6° difference and for the inboard section about3°.

FIGS. 5-7 show one of the blades 10 of the fan of FIG. 1 in greaterdetail. The blade is seen to have its root end 11 mounted to the fanmotor rotor hub 12 with its tip end 13 located distally of the hub. Thehub rotates about the axis of the downrod from the ceiling as shown inFIG. 1 which is substantially vertical. As most clearly noted by theblade centerline 15, the blade has a 0° dihedral at its root end 11 anda 10° dihedral d^(t) at its tip 13. The fan blade here is continuouslyarched or curved from end to end so that its dihedral is continuouslychanging from end to end. As shown by the air flow distribution brokenlines in FIG. 1 this serves to distribute air both directly under thefan as well as in the ambient air space that surrounds this space.Conversely, fans of the prior art have mostly directed the airdownwardly beneath the fan with air flow in the surrounding space beingindirect and weak. Though those fans that have had their blades inclinedat a fixed dihedral throughout their length have solved this problem,such has been at the expense of diminished air flow directly under thefan.

The blade dihedral may increase continuously from end to end. However,it may be constant near its root end and/or near its tip with its archedor curved portion being along its remainder. Indeed, the most efficientdesign, referred to as the gull design, has a 0° dihedral from its rootend to half way to its tip, and then a continuously increasing dihedralto its tip where it reaches a dihedral of 10°. In the preferredembodiment shown the blade root end has a 0° dihedral and its tip a 10°dihedral. However, its root end dihedral may be less than or more than0° and its tip less than or more than 10°. Fan size, power, height andapplication are all factors that may be considered in selecting specificdihedrals.

The fan was tested at the Hunter Fan Company laboratory which iscertified by the environmental Protection Agency, for Energy StarCompliance testing. The fan was tested in accordance with the EnergyStar testing requirements except that air velocity sensors were alsoinstalled over the top and close to the fan blades. This allowed for themeasurement of air velocity adjacent to the fan blade. During thetesting it was determined that the velocity of the air is different atvarious places on the fan blades from root end to tip end. Testparameters are shown in FIG. 4. The actual test results appear inTable 1. TABLE 1 Avg. Vel. Air V Rotor Resultant Resultant Deg/ SensorFPM FPS Vel FPS Vel Angle inch 0 283 4.7 22.7 23.2 11.7 1 303 5.1 24.424.9 11.7 0.07 2 320 5.3 26.2 26.7 11.5 0.16 3 325 5.4 27.9 28.4 11.00.54 4 320 5.3 29.7 30.1 10.2 0.79 5 313 5.2 31.4 31.8 9.4 0.76 6 3085.1 33.1 33.5 8.8 0.63 7 305 5.1 34.9 35.3 8.3 0.51 8 290 4.8 36.6 37.07.5 0.77 9 275 4.6 38.4 38.7 6.8 0.71 10 262 4.4 40.1 40.4 6.2 0.60 11235 3.9 41.9 42.0 5.3 0.87 12 174 2.9 43.6 43.7 3.8 1.54 13 132 2.2 45.445.5 2.8 1.03

Comparative test results appear in Table 2 where blade 1 was the new onejust described with a 10° fixed dihedral, blade 2 was a Hampton BayGossomer Wind/Windward blade of the design taught by U.S. Pat. No.6,039,541, and blade 3 was a flat blade with a 15° fixed angle ofattack. The tabulated improvement, was in energy efficiency aspreviously defined. TABLE 2 Improvement Improvement Over ImprovementOver With Hampton Over Without Hampton Improvement Blade Motor CylinderBay Standard cylinder Bay Outside 4 ft 1 172 × 18 AM 12,878 21% 29%37,327 24% 27% 2 188 × 15 10,639 NA  6% 30,034 NA NA 3 172 × 18 AM10,018 −6% NA 28,000 −7% −7%

With reference next to FIGS. 8-10, there is shown a ceiling fan havingblades incorporating the present invention in another preferred form.Here, it is seen that the blade is demarked to have six sectionsalthough the blade is, of course, of unitary construction. Here the24-inch long blade has six sections of various lengths. The firstsection adjacent the root is approximately 3 inches, the second sectionis approximately 5 inches, the third section is approximately 2 inches,the fourth section is approximately 7 inches the fifth section isapproximately 7 inches and the sixth section is approximately 1 inch.All sections except for the first section are twisted as is evident inFIGS. 8-10. However the rate of twist is nonuniform. The twist or angleof attack deceases from inboard portion of the third section to the tipend. This decrease, however, which is also apparent in FIG. 1, is at twodifferent rates. In the third section the change in twist rate isapproximately 0.5° per inch. For the fourth, fifth and sixth sections itis approximately 0.7° per inch. Of course there is a small transitionbetween the sections of negligible significance. Thus, in FIG. 10 thethird section commences at a 24° angle of attack and ends at a 23° angleof attack, thus there is an 1° difference in angle of attack from oneend of the third section to its other (1° per inch×2 inches). The fourthsection commences at a 23° angle of attach and ends at a 18° angle ofattack, thus there is an 5° difference in angle of attack from one endof the fourth section to its other (5° per inch×7 inches). The fifthsection commences at a 18° angle of attach and ends at a 14° angle ofattack, thus there is an 4° difference in angle of attack from one endof the fifth section to its other (4° per inch×6 inches)

It should be understood that the second embodiment is similar inprinciple to the first embodiment shown in FIG. 1 except for the factthat the blade root commences horizontally then dips down beforecommencing the blade's normal angle of attack. This difference stemsfrom the blade being mounted generally perpendicular to the motor axisat the actual root rather than the blade initially being set at anangled to the motor axis, i.e., the blade initially having an angle ofattack. However, it should be understood that in the second embodimentthe “root” may simply be thought of as being positioned outboard fromthe actual “root” or actual inboard end of the blade. Thus, as usedherein the term “root” may also be considered the position along the fanadjacent the fan axis wherein the angle of attack to produce the desiredair flow commences, which in this embodiment is the inboard portion ofthe third section.

It thus is seen that a ceiling fan now is provided of substantiallyhigher energy efficiency than those of the prior art and with enhancedflow distribution. The fan may of course be used in other locations suchas a table top. Although it has been shown and described in itspreferred form, it should be understood that other modifications,additions or deletions may be made thereto without departure from thespirit and scope of the invention as set forth in the following claims.

1. A high efficiency ceiling fan having a plurality of fan bladesmounted for rotation about a fan axis of blade rotation and with theblades having a greater angle of attack at a location adjacent said fanaxis than distally said fan axis with the rate of change in angle ofattack therebetween being non-uniform, the blade angle of attackdecreasing continuously from adjacent said fan axis to distally said fanaxis, and therein the blade angle of attack decreases at a plurality ofincrementally different rates from adjacent said fan axis to distal saidfan axis.
 2. The high efficiency ceiling fan of claim 1 wherein theblade angle of attack decreases in two different incrementally fixedrates.
 3. The high efficiency ceiling fan of claim 2 wherein the bladeangle of attack decreases approximately 0.5 degrees per inch adjacentsaid fan axis to approximately 0.7 degrees per inch distally said fanaxis.
 4. A high efficiency ceiling fan having a plurality of fan bladesmounted for rotation about a fan axis of blade rotation and with theblades being twisted at a plurality of fixed rates of decrease as theyextend from a position adjacent the fan axis at a twist rate thatdecreases non-uniformly from a position adjacent the motor to the bladetip end.
 5. The high efficiency ceiling fan of claim 4 wherein the bladeangle of attack decreases in two different incrementally fixed rates. 6.The high efficiency ceiling fan of claim 5 wherein the blade angle ofattack decreases approximately 0.5 degrees per inch adjacent said fanaxis to approximately 0.7 degrees per inch distally said fan axis.